BEIRUT — Heavy fighting raged around the strategic Syrian border town of Qusair and the capital Damascus on Monday and further reports surfaced of chemical weapons attacks by President Bashar al-Assad’s forces on rebel areas.

Intensified government offensives are widely seen as a bid to strengthen Assad’s position before a peace conference proposed by the United States and Russia for next month.

Also on Monday, a sniper killed a well-known Syrian journalist working for a pro-government television channel near the Lebanese-Syrian border, the state news agency said.

Yara Abbas, a reporter for the al-Ikhbariya news channel, was killed near Debaa airport in Homs province. Forces loyal to Assad there have been trying to recapture the base from the rebels seeking to oust him.

Syria TV said Abbas, in her mid-20s, was targeted by “terrorists,” the term commonly used by Assad supporters to describe the rebels.

The Syrian Observatory for Human Rights, a pro-opposition monitoring group, said several members of her television team were also wounded in the attack.

The Syrian military, meanwhile, pounded eastern suburbs of Damascus with air strikes and artillery and loud explosions echoed around al-Nabak, 50 miles north of the capital, where fighting has cut the highway running north to the central city of Homs, the pro-opposition Syrian Observatory for Human Rights group said.

Opposition activists said Syrian troops backed by Lebanese Hezbollah fighters were pressing a sustained assault on Qusair, a town long used by insurgents as a way station for arms and other supplies from Lebanon.

For Assad, Qusair is a crucial link between Damascus and loyalist strongholds on the Mediterranean coast. Recapturing the town could also sever connections between rebel-held areas in the north and south of Syria.

Hezbollah’s deepening involvement in Qusair has raised the prospect of renewed civil war in Lebanon, where two rockets hit the Shiite Muslim movement’s stronghold in south Beirut on Sunday and one was fired from south Lebanon toward Israel.

A Lebanese security source said another 107mm rocket, which did not go off, had been aimed at Beirut airport. The launch sites were near Aitat, in the hills just south of the capital.

U.N. Secretary-General Ban Ki-moon voiced “deep concern” at Hezbollah’s admitted combat role and the risk that the Syrian conflict will spill into Lebanon and other neighbouring states.

The U.S.-Russian initiative so far appears only to have intensified the violence, especially around Qusair and Damascus.

In Harasta, an eastern Damascus suburb largely under rebel control, dozens of people were afflicted by respiratory difficulties after an apparent overnight chemical attack, according to opposition sources. Video showed victims lying on the floor of a room, breathing from oxygen masks.

The sides in the conflict, now in its third year, have accused each other of using chemical weapons. France’s Le Monde newspaper published first-hand accounts on Monday of apparent chemical attacks by Assad’s forces in April.

The newspaper said one of its photographers had suffered blurred vision and breathing problems for four days after an attack on April 13 on the Jobar front, in central Damascus.

Another video from Harasta overnight showed at least two fighters being put into a van, their eyes watering and struggling to breathe while medics put tubes into their throats.

It was not possible to verify the videos independently.

Syria, which is not a member of the anti-chemical weapons convention, is believed to have one of the world’s last remaining stockpiles of undeclared chemical arms.

French Foreign Minister Laurent Fabius told reporters in Brussels there was “increasingly strong evidence of localized use of chemical weapons” in Syria and said Paris would consult its partners on what action ought to be taken.